Gas Buying Tips

[NickCats]

Not sure if this is legit or not ( got it in email ) but I thought it was interesting :

I've been in petroleum pipeline business for about 31 years, currently working for the Kinder-Morgan Pipeline here in San Jose, CA. We deliver about 4 million gallons in a 24-hour period from the pipe line; one day it's diesel, the next day it's jet fuel and gasoline. We have 34 storage tanks here with a total capacity of 16,800,000 gallons. Here are some tricks to help you get your money's worth.

1. Fill up your car or truck in the morning when the temperature is still cool. Remember that all service stations have their storage tanks buried below ground; and the colder the ground, the denser the gasoline. When it gets warmer gasoline expands, so if you're filling up in the afternoon or in the evening, what should be a gallon is not exactly a gallon. In the petroleum business, the specific gravity and temperature of the fuel (gasoline, diesel, jet fuel, ethanol and other petroleum products) are significant. Every truckload that we load is temperature-compensated so that the indicated gallonage is actually the amount pumped. A one-degree rise in temperature is a big deal for businesses, but service stations don't have temperature compensation at their pumps.

2. If a tanker truck is filling the station's tank at the time you want to buy gas, do not fill up; most likely dirt and sludge in the tank is being stirred up when gas is being delivered, and you might be transferring that dirt from the bottom of their tank into your car's tank.

3. Fill up when your gas tank is half-full (or half-empty), because the more gas you have in your tank the less air there is and gasoline evaporates rapidly, especially when it's warm. (Gasoline storage tanks have an internal floating 'roof' membrane to act as a barrier between the gas an d the atmosphere, thereby minimizing evaporation.)

4. If you look at the trigger you'll see that it has three delivery settings: slow, medium and high. When you're filling up do not squeeze the trigger of the nozzle to the high setting. You should be pumping at the slow setting, thereby minimizing vapors created while you are pumping. Hoses at the pump are corrugated; the corrugations act as a return path for vapor recovery from gas that already has been metered. If you are pumping at the high setting, the agitated gasoline contains more vapor, which is being sucked back into the underground tank so you're getting less gas for your money.
Hope this will help ease your 'pain at the pump'.

Nick

The part about not filling up during a tanker fill is practical. Everything else is splitting hairs IMO, and not really worth the trouble. My guess is everything else would account for less than .25¢ savings.


On a large scale like refineries, it does add up. My brother in law works in the fuel testing facility at BA, and told me about cold filling years ago. I still have never done it.

[rick3000]

That is some interesting information especially #1, but the others are bit out there. I am not saying #2, #3, and #4 are not true but it doesn't seem like they make a huge difference considering just about every person ignores them, and does okay.

[blinkwatt]

Good stuff Nick!

[JCL12]

Ok - I pretty much do none of this!

If I were to buy gas in the AM, pump slowly, etc would there be any measurable change? How much?

[indydave]

The temperature thing is probably only true for a short period of time after the gas is delivered. Once the gas in in the tanks underground, I doubt that there's much temperature variation over the course of a day.

Here's another interesting Gasoline fact: Ethanol has only about 70% the energy density of gasoline. Vehicles that run E85 typically get 25-30% less MPG than on Gasoline.

This effect is also present when you buy gas that's 10% Ethanol. Since that 10% of the fuel has only 70% of the energy of the rest the rest of the gasoline, the overall energy density of the fuel (compared to gasoline) is (.90*100%)+(.10*70%)=97%. This means your gas mileage WILL be reduced by 3% if you use the 10% Ethanol blend. If your Boxster gets 25.00 MPG on regular Gasoline, it will get 24.25 MPG on the 90/10 blend.

The 90/10 blends are a bad deal unless the price is less than 97% of the price of 100% Gasoline: If Gas is $3.00 a gallon, you'd have to buy the 90/10 blend for $2.91 or less to break even.

There are some other things to worry about with ethanol, too, but the economics alone usually make it a poor bargain.

[blue2000s]

Originally Posted by NickCats

Not sure if this is legit or not ( got it in email ) but I thought it was interesting :

I've been in petroleum pipeline business for about 31 years, currently working for the Kinder-Morgan Pipeline here in San Jose, CA. We deliver about 4 million gallons in a 24-hour period from the pipe line; one day it's diesel, the next day it's jet fuel and gasoline. We have 34 storage tanks here with a total capacity of 16,800,000 gallons. Here are some tricks to help you get your money's worth.

1. Fill up your car or truck in the morning when the temperature is still cool. Remember that all service stations have their storage tanks buried below ground; and the colder the ground, the denser the gasoline. When it gets warmer gasoline expands, so if you're filling up in the afternoon or in the evening, what should be a gallon is not exactly a gallon. In the petroleum business, the specific gravity and temperature of the fuel (gasoline, diesel, jet fuel, ethanol and other petroleum products) are significant. Every truckload that we load is temperature-compensated so that the indicated gallonage is actually the amount pumped. A one-degree rise in temperature is a big deal for businesses, but service stations don't have temperature compensation at their pumps.

2. If a tanker truck is filling the station's tank at the time you want to buy gas, do not fill up; most likely dirt and sludge in the tank is being stirred up when gas is being delivered, and you might be transferring that dirt from the bottom of their tank into your car's tank.

3. Fill up when your gas tank is half-full (or half-empty), because the more gas you have in your tank the less air there is and gasoline evaporates rapidly, especially when it's warm. (Gasoline storage tanks have an internal floating 'roof' membrane to act as a barrier between the gas an d the atmosphere, thereby minimizing evaporation.)

4. If you look at the trigger you'll see that it has three delivery settings: slow, medium and high. When you're filling up do not squeeze the trigger of the nozzle to the high setting. You should be pumping at the slow setting, thereby minimizing vapors created while you are pumping. Hoses at the pump are corrugated; the corrugations act as a return path for vapor recovery from gas that already has been metered. If you are pumping at the high setting, the agitated gasoline contains more vapor, which is being sucked back into the underground tank so you're getting less gas for your money.
Hope this will help ease your 'pain at the pump'.

Nick

These are all sound recommendations based in fact.

[markab986]

Possibly good advice, although I can't confirm or deny any of it.

My opinion(s)...

1) If it's underground storage, I can't see any temp benefit

2) a) There are filters (should be ) in place for this filthy problem

b) Just how long should you wait for the "stirred up" content to settle (a several thousand gallon tank would take x period of time)?

3) Most modern vehicles have a vapor recovery system in place in the fuel system...but...I would have to admit the chance of condensation in your tank would most likely be lower with a higher level.

4) The vapor recovery system is "sucking" vapor that is present in your tank already and is preventing "smog" from unburned HC emissions venting your tank into the open atmosphere...any container that is taking on liquid is purging a gas, as it is being filled. I doubt that it helping speed up the refuel process ala CART racing


...finally, the % of ethanol in fuel is "only" labeled IF it contains MORE than 10% (although this may vary from state to state)

just my $.02

[boxstershorts]

In Canada, or more precisely: in Montreal, pump pricing is corrected to 15°C.

Secondly:
Trying to gain from vapours by gasing up in the morning or pumping slowly isn't going to pay for your Porsche. So don't waste your time pumping slowly, spend it driving...

[cfos]

So... if the temp thing is true...

Suppose you gas up in the afternoon and go straight home and park it in the garage. Ambient temperature, in most parts of the country drop overnight, thus, you would argue that you would have more gas in your car in the morning, right? If so, would that cancel out the afternoon shortage?

[JackG]

Originally Posted by cfos

So... if the temp thing is true...

Suppose you gas up in the afternoon and go straight home and park it in the garage. Ambient temperature, in most parts of the country drop overnight, thus, you would argue that you would have more gas in your car in the morning, right? If so, would that cancel out the afternoon shortage?

Actually, the opposite. If you filled up with warm gas, then parked it full and it cooled off, the tank would not be full in the morning. Gas expands when hot, and contracts when cool.

I agree with the others that say the temp thing actually doesn't make any appreciable difference. The temperature of the underground storage tanks stays pretty consistent from day to night, the air entering the tank as the gas is pumped out is small compared to the existing gas and air in the tank, so it heats/cools to the tank's temp quickly. It also takes a fairly large swing in temps to make any real difference in the relatively small amounts that we put in our cars.

In the end we're talking about a couple of pennies worth... I've got better things to worry about.

[porsche986spyder]

Isn't the gas cap on our cars pressure sensitive? So to me, #3 sounds a bit silly. Whenever you open your gas cap up, you can hear the vapor/pressure release. Sounds like a very tight seal and I can't see how any gas would be evaporating from inside our tanks. Unless you don't turn the cap and hear the clicking noise, you should be fine in this area. :dance:

Originally Posted by markab986

2) a) There are filters (should be ) in place for this filthy problem

You'd be surprised how much crap can come out of a gas pump. I learned the hard way by not changing the fuel filter on a beater car of mine for over with 100k miles. Eventually the fuel filter plugged and killed the fuel pump by over stressing it. Also, I looked in my portable gas can that fills my lawn mower. I empty it out in the winter and there was some debris on the bottom. I've only filled it twice ever ~5 gallons. I made sure it was clean beforehand, and I am very clean when I fill. Little chance I introduced the debris when corking/uncorking it.


This all makes me a bit nervous as my 02 S doesn't have a user serviceable fuel filter...

[IowaS]

Originally Posted by indydave

The temperature thing is probably only true for a short period of time after the gas is delivered. Once the gas in in the tanks underground, I doubt that there's much temperature variation over the course of a day.

Here's another interesting Gasoline fact: Ethanol has only about 70% the energy density of gasoline. Vehicles that run E85 typically get 25-30% less MPG than on Gasoline.

This effect is also present when you buy gas that's 10% Ethanol. Since that 10% of the fuel has only 70% of the energy of the rest the rest of the gasoline, the overall energy density of the fuel (compared to gasoline) is (.90*100%)+(.10*70%)=97%. This means your gas mileage WILL be reduced by 3% if you use the 10% Ethanol blend. If your Boxster gets 25.00 MPG on regular Gasoline, it will get 24.25 MPG on the 90/10 blend.

The 90/10 blends are a bad deal unless the price is less than 97% of the price of 100% Gasoline: If Gas is $3.00 a gallon, you'd have to buy the 90/10 blend for $2.91 or less to break even.

There are some other things to worry about with ethanol, too, but the economics alone usually make it a poor bargain.

Dont get me going about the complete farce known as ethanol...anyone that thinks it is "renewable" and eco friendly is sorely mistaken...

[brp987]

hey IowaS - I'd like to get you going re: ethanol. It is a fraud isn't it? It actually results in increased use of petroleum, right? It's unnecessary for meeting emissions requirements, right? A political solution to a scientific problem? But a lot of happy corn farmers out there in Iowa though, I'll bet.